Improving Pre-Analytical Practices in Blood Gases and Other Analytes Webinar, March 30, 2021

Responses from Speaker John Ancy to Questions Submitted by Webinar Attendees

  1. Many of our 3mL syringes are only filled about 1.5mL. Should partially filled 1mL or 3mL tubes be rejected due to altered heparin concentrations?

    When using dry lithium or zinc heparin-formulation syringes for reporting blood gas, CO-Oximetry and metabolite results, there is no issue with underfilled syringes.  However, for electrolyte results, this becomes more complex, as heparin binds Na+ and Ca++, and excessive heparin concentrations can falsely lower Na+ and Ca++ results.

    There are two approaches to limiting heparin-related errors for Na+ and Ca++.  1) Use balanced heparin formulations with small amounts of Na+ and Ca++ added to offset heparin cation binding.  2) Use low-concentration heparin formulations, which decreases cation binding.

    For non-balanced heparin formulations, final heparin concentrations <20IU/mL are generally recommended. Failure to fill low-heparin syringes to recommended capacity can increase final heparin concentration and falsely lower Na+ and Ca++. Whereas, underfilling balanced heparin syringes can falsely increase Na+ and Ca++, due to added cations in the formulation. For electrolyte reporting, filling syringes to >50% is generally recommended. However, specific guidelines in package inserts should always be reviewed. Sample rejection policies should be determined by each laboratory. 

     

  2. Due to supply issues, our facility started using 1mL syringes. Where can I find 1mL syringe instructions to educate my staff?

    Package inserts usually offer instructions on handling recommendations. Typically, suggested fill volume, heparin formulation and instructions on air removal and capping are included. It is known that 1mL syringes require more vigorous rocking, for heparin dissolution into the sample. This applies to both initial mixing and re-mixing, just prior to sample analysis. 
     

  3. Vacutainer tubes are vacuumed-sealed. Does air enter with the blood when drawn?  And, does the air that enters affect the sample?

    Vacutainers are not completely air-free. It is important to completely fill vacutainers when used for blood gas or Ca++ analysis. Vacutainers should not be used for arterial sampling. When used for venous samples, pO2 is not useful for oxygenation assessment.
     

  4. What is recommended for temperature correction of blood gases?

    Temperature correction of blood gases is generally not recommended. This is primarily due to result reference ranges, which are established at 37°C, with no published ranges at other temperatures. 

    Interpreting temperature-corrected values using 37°C reference ranges could result in mistreatment. There is some indication that temperature correction, or pH-STAT blood gas management, could be valuable when using therapeutic hypothermia (32–34°C) for brain hypoxia prevention. Non-temperature correction is called alpha-STAT. If using temperature correction, it is advisable to provide uncorrected and temperature-corrected values on the report. It should also be noted on the report that values are based on 37°C ranges.
     

  5. What is the difference between ionized calcium (Ca++) measured in whole blood in a tube (dry lithium heparin 18IU/mL) versus serum?

    Serum and whole blood Ca++ are considered equivalent. It is very important to fill collection devices to full capacity for Ca++ measurements. If air is left in collection device, pCO2 will decrease with a subsequent increase in pH. With increased pH, blood proteins have higher affinity for Ca++, which falsely reduces Ca++ concentration.
     

  6. Some hospitals run venous blood gases in heparinized blood tubes. Is this acceptable? 

    In most instances, venous samples are considered reliable for acid-base evaluation. Electrolyte and metabolite values from venous samples are equivalent to values from arterial samples. Venous samples are acceptable for total Hb, methemoglobin (MetHb), and carboxyhemoglobin measurement. However, venous pO2 and O2Hb values do not reflect true oxygenation status. 
     

  7. Do you have guidelines for MetHb stability?

    The heme group iron in MetHb is oxidized to Fe3+ rather than Fe2+, as with oxyhemoglobin or reduced hemoglobin. In stored samples, Hb spontaneously oxidizes to MetHb(Fe3+) . MetHb is stable for one hour at room temperature and four hours on ice, and it increases significantly over time, and at extreme storage temperatures.

     

  8. Do you recommend the use of mixing fleas with capillary samples?

    I am not aware of any studies that have demonstrated the superiority of mixing fleas versus the immediate rolling of capillary tubes for heparin mixing. However, use of mixing fleas increases preparation time, biohazard exposure, room air exposure and potentially can cause hemolysis. Immediate roll mixing for a minimum of 30 seconds after tube ends are capped, and remixing prior to analysis, can be very effective in preventing sample clotting.
     

  9. Can clot catchers be used with the GEM Premier 5000 system?

    Clot catchers are not recommended or required for GEM Premier systems. Mixing samples immediately post-draw with a rocking motion for heparinized syringes, or with a rolling motion for capillary tubes, is very effective for clot/micro-clot prevention. Intelligent Quality Management (iQM) and iQM2 detect and correct clots and micro-clots when inadvertently introduced into the system.
     

  10. How do micro-clots affect test result quality?

    Micro-clots have been demonstrated to affect the accuracy of results. The larger the micro-clot, the greater its potential to affect the sensor and result accuracy. A study, published in 2003, indicated that micro-clots can cause significant error at medical-decision levels for nearly all analytes. Good sample-handling practices greatly reduce the potential for micro-clot formation. Immediate and thorough mixing (rocking motion for a minimum of 30 seconds) is very effective in preventing micro-clot formation. IL recognizes the importance of the error potential from micro-clots and other sources. iQM and iQM on GEM Premier analyzers can detect micro-clots, helping prevent erroneous results reporting.

     

  11. Does the Joint Commission require 3 levels of QC for each new blood gas cartridge before it can be used? 

    The Joint Commission standard (3/14/2021) for blood gas controls/frequency (QSA.06.02.01) states:

    The laboratory verifies the operation of each blood gas testing instrument through the use of quality control materials.
    Elements of performance:
    1. The laboratory tests at least two different levels of quality control materials for blood gas testing each day the procedure is performed. The combination of controls and calibrators used each day of testing are rotated to check normal, alkalosis, and acidosis levels. The quality control results are documented.                   
    2. The laboratory tests at least one level of quality control material for each eight hours of patient blood gas testing. The quality control results are documented.
    Note: The laboratory should attempt to perform quality control testing as close to 8-hour intervals as possible. A range may be specified in written policy, such as within 15 minutes before or after the 8-hour mark, providing a 30-minute window. Ranges in excess of +/- 30 minutes that produce a window of more than an hour do not meet the intent of this element of performance.              
    3. The laboratory tests at least one level of quality control material each time patients are tested unless automated instrumentation verifies calibration internally every 30 minutes.

    CMS released a clarification notice, specifically addressing what is required and acceptable for blood gas testing quality control. The Joint Commission and CAP stated that they are aligned with CMS’s definition. 

    IL requirements include appropriate calibration valuation product (CVP) for the GEM Premier 4000 system and auto PAK validation (APV) for the GEM Premier 5000 system.  The Process Control Solution type, frequency and schedule are included in the Operators Manual, and they meet or exceed the specifications above.

    All Process Control Solutions for GEM Premier blood gas systems follow the same fluidic pathway as the patient sample.

    As always, it is best to have any specific accreditation question addressed directly by the respective accreditation agency.
     

  12. How can we convince nursing staff who collect venous and arterial samples that their technique can affect test results? 
       
    Education is key. There are a variety of open-access publications on potential medical errors due to inappropriate blood gas-sample handling. Additionally, IL offers a self-study presentation “Pre-analytical Quality in Blood Gas Testing,” with explanatory notes (available through your local representative). Hospitals have incorporated this presentation into their e-learning platform as part of blood gas training. Today's webinar, “Improving Pre-analytical Practices for Blood Gases and Related Analytes”, is also available on Werfen Academy. Click here to watch the recording of this webinar.